Optical communication module, manufacturing method therefor, and optical transceiver

ABSTRACT

A manufacturing method of an optical communication module for manufacturing the optical communication module, including the sequentially performed steps of: (1) mounting a light-emitting element and a light-receiving element on a side surface of a sub-mount substrate and mounting the sub-mount substrate on a printed circuit board such that the light-emitting and -receiving directions of the light-emitting element and light-receiving element are parallel to the printed circuit board; (2) aligning an optical waveguide; and (3) dropping resin solution on an area of the sub-mount substrate including an optical waveguide end and the light-emitting element or the light-receiving element, and curing the resin solution. According to the present invention, it is possible to provide an optical communication module which can be made thin, small and cheap.

TECHNICAL FIELD

The present invention relates to an optical communication module formedby joining a light-emitting element and a light-receiving element to anoptical waveguide, manufacturing method therefor, and an opticaltransceiver.

Priority is claimed on Japanese Patent Application No. 2007-127810,filed May 14, 2007, the content of which is incorporated herein byreference.

This application is a continuation application based on a PCT PatentApplication No. PCT/JP2008/053036, filed Feb. 22, 2008, whose priorityis claimed on Japanese Patent Application No. 2007-127810 filed May 14,2007, the entire content of which are hereby incorporated by reference.

BACKGROUND ART

An optical communication module is preferably small in size and lowcost. In recent years, a VCSEL (vertical cavity surface emitting laser)has been examined as a light-emitting element used in an opticalcommunication module. For convenience of the manufacturing process, abare chip of the VCSEL generally has a configuration with a surface witha light-emitting portion and a back surface of the light-emittingportion where an anode and a cathode are provided, as shown in FIG. 1.In FIG. 1, reference numeral 1 denotes a cathode, reference numeral 2denotes an anode, reference numeral 3 denotes a light-emitting portion,reference numeral 4 denotes a VCSEL, and reference numeral 5 denotes abonding wire. In this illustration, for the anode 2, the entire backsurface of the chip is a solid electrode. In addition, without beinglimited to this illustration, there is also a chip in which the anode 2and the cathode 1 are opposite to those described above.

Accordingly, when manufacturing an optical communication module bymounting a light-emitting element, such as the VCSEL 4, on the printedcircuit board with a known structure, light is emitted only in thedirection perpendicular to the printed circuit board. In addition, thesame is true for a light-receiving element; light is received only inthe direction perpendicular to the printed circuit board.

In order to mount such a light-emitting element and a light-receivingelement on the printed circuit board and to join the optical waveguideto them, methods such as the following (A) and (B) are used.

(A) Method of disposing an optical waveguide 11 vertically with respectto a printed circuit board 15 on which an IC 12 and a VCSEL 14 aremounted and joining it to a light-emitting portion 13 of the VCSEL14, asshown in FIG. 2.

(B) Method of disposing an optical waveguide 21 horizontally withrespect to a printed circuit board 25 on which an IC 22 and a VCSEL 24are mounted, providing a mirror with an inclination of 45° and the likeat the tip of the optical waveguide 21, and reflecting the light emittedfrom a light-emitting portion 23 of the VCSEL 24 by using the mirror sothat the light is incident on the optical waveguide 21 and is coupledthereto, as shown in FIG. 3.

The known techniques regarding the present invention, for example, aredisclosed in Patent Documents 1 to 4.

In recent years, optical wiring has been applied to high-speedcommunication apparatuses such as servers, optical wiring inautomobiles, and small electronic apparatuses such as mobile phones. Asefforts are being made to reduce the size and cost of such apparatuses,there is also a strong demand for miniaturization and low cost ofoptical transceivers. As light-emitting elements used for the opticaltransceiver, a laser diode (LD), a light-emitting diode (LED), and avertical cavity surface emitting laser (VCSEL) are used. In addition, aphotodiode is used as a light-receiving element. A fiber type or sheettype waveguide is used as the optical waveguide, and are made of silicaglass, a polymer, or the like. For the structure and method of joining alight-emitting or receiving element to an optical waveguide in anoptical transceiver, various methods have been examined (for example,refer to Patent Documents 5 to 8).

[Patent Document 1] Japanese Patent Application Laid-Open PublicationNo. 2004-309570

[Patent Document 2] Japanese Unexamined Patent Application, FirstPublication No. 2005-134600

[Patent Document 3] Japanese Unexamined Patent Application, FirstPublication No. 2004-253638

[Patent Document 4] Japanese Unexamined Patent Application, FirstPublication No. 2005-284248

[Patent Document 5] Japanese Unexamined Patent Application, FirstPublication No. 2006-11179

[Patent Document 6] Japanese Unexamined Patent Application, FirstPublication No. 2005-202025

[Patent Document 7] Japanese Patent Publication No. 3392748

[Patent Document 8] Japanese Unexamined Patent Application, FirstPublication No. 8-220368

DISCLOSURE OF THE INVENTION Problem that the Invention is to Solve

In the optical communication modules having the known structuresdisclosed in Patent Documents 1 to 4, however, the maximum height on thesubstrate increases inevitably when joining the light-emitting elementto the optical waveguide. As a result, there is a problem in that such amodule is difficult to be mounted in mobile consumer products, such asminiaturized communication apparatuses, mobile phones, and notebookcomputers.

Moreover, in the structure where the 45° mirror is provided on the endof the optical waveguide, there is a problem in that the production costis increased even though the height on the substrate can be slightlylower.

In addition, there are the following problems in the known techniquesdisclosed in Patent Documents 5 to 8. As shown in FIG. 3, PatentDocument 5 discloses a method for disposing the optical waveguide 21horizontally with respect to the printed circuit board 25 on which theIC 22 and the VCSEL 24 are mounted, providing a mirror with aninclination of 45° and the like at the tip of the optical waveguide 21,and reflecting the light emitted from the light-emitting portion 23 ofthe VCSEL 24 by the mirror so that the light is incident on the opticalwaveguide 21 and is coupled thereto. In this method, however, there is aproblem in that it takes a significant amount of time and cost to formthe 45° mirror. In addition, there is also a problem in that it takes asignificant amount of time and cost to perform optical axis alignment ofthe VCSEL 24 and the optical waveguide 21 due to diffusion on thesurface of the 45° mirror and extension of the optical path length.Since a certain area is required for attaching a mirror and a lens, orspace (focal distance) for operating the mirror and the lens, it is notcompatible with miniaturization.

Patent Document 6 discloses a method for making the light emitted from alight-emitting device incident on a waveguide, monitoring the output atthe emission end of the waveguide with a light-receiving device, andmoving the light-emitting device, the light-receiving device, and thewaveguide relative to each other and fixing them such that the output ismaximized. However, in this method, it takes a significant amount oftime to make adjustments. Particularly when a plurality of opticalwaveguides is connected, the efficiency is low, and this results in anincrease in cost.

Patent Document 7 uses an LD as a light source. The LD is mounted on thesilicon substrate (equivalent to a sub-mount) and the entire LD, thewaveguide end, and a part of the bonding wire are covered by a resin.However, the silicon substrate is for heat dissipation but is not foradjusting the light-emitting direction of the LD. Since the entiresilicon substrate (sub-mount) is not covered with the resin, it does nothave the function of improving the bonding strength of the siliconsubstrate to the stem (equivalent to a printed circuit board) either. Inaddition, since a part of the bonding wire is exposed from the resin,there is no function of protecting the bonding wire. In addition, sincethe VCSEL is not used, power consumption is high and it is expensive.

Patent Document 8 uses an LD as a light source. The LD is mounted on thesilicon substrate (equivalent to the sub-mount) and the entire LD, thewaveguide end, and the entire silicon substrate are covered by a resin.However, the purpose of the silicon substrate is heat dissipation andnot to adjust the light-emitting direction of the LD. In addition, sincethe VCSEL is not used, power consumption is high and it is expensive.

The present invention has been made in view of the above situation, andhas an object of providing an optical communication module and anoptical transceiver which can be made to be thin, small and cheap.

Means for Solving the Problem

In order to achieve the above-described object, the present inventionprovides an optical communication module including: a printed circuitboard; a sub-mount substrate in which one or both a light-emittingelement and a light-receiving element are mounted on a side surfacethereof; and an optical waveguide provided between the light-emittingelement and the light-receiving element so as to be able to be opticallycoupled with the light-emitting element and the light-receiving element.The light-emitting element and the light-receiving element are mountedon the printed circuit board with the sub-mount substrate therebetweensuch that the light-emitting and receiving directions of the elementsare parallel to the printed circuit board. The light-emitting elementand the light-receiving element of the sub-mount substrate and ends ofthe optical waveguide adjacent to the elements are covered by a resin.

In addition, the present invention provides a manufacturing method of anoptical communication module for manufacturing the optical communicationmodule, including the sequentially performed step of: (1) mounting alight-emitting element and a light-receiving element on a side surfaceof a sub-mount substrate and mounting the sub-mount substrate on aprinted circuit board such that the light-emitting and receivingdirections of the light-emitting element and light-receiving element areparallel to the printed circuit board; (2) aligning an opticalwaveguide; and (3) dropping a resin solution on an area of the sub-mountsubstrate portion including an optical waveguide end and thelight-emitting element or the light-receiving element and of curing theresin solution.

In addition, the present invention provides an optical transceiverincluding: a printed circuit board; a sub-mount substrate in which oneor both a light-emitting element and a light-receiving element aremounted on a side surface thereof; and an optical waveguide providedbetween the light-emitting element and the light-receiving element so asto be able to be optically coupled with the light-emitting element andthe light-receiving element. The light-emitting element and thelight-receiving element each have structures in which a surface incontact with the substrate and a surface through which light is emittedor received are at the top and bottom positions and the light is emittedor received in a direction perpendicular to the mounted substrate. Thelight-emitting element and the light-receiving element are mounted onthe printed circuit board with the sub-mount substrate therebetween suchthat the light-emitting and receiving directions of the elements are notperpendicular to the printed circuit board. The entire sub-mountsubstrate, the entire light-emitting element, the entire light-receivingelement, and ends of the optical waveguide adjacent to the elements arecollectively covered by a resin.

Advantage of the Invention

The optical communication module of the present invention has aconfiguration where the light-emitting element and the light-receivingelement are mounted on the printed circuit board through the sub-mountsubstrate such that the light-emitting and receiving directions of theelements are parallel to the printed circuit board and thelight-emitting element and the light-receiving element of the sub-mountsubstrate and the ends of the optical waveguide are fixed by coveringthem with a resin. Accordingly, since it is possible to emit and receivethe light in a direction parallel to the printed circuit board,reduction in height (thickness) and miniaturization of the opticalcommunication module can be realized.

In addition, since additional optical components, such as mirrors forchanging the light-emitting and receiving directions, are not necessary,a small and thin optical communication module can be cheaply provided.

According to the manufacturing method of the optical communicationmodule of the present invention, a thin and small optical communicationmodule can be produced efficiently and cheaply.

The optical transceiver of the present invention has a structure wherean element is used which has a structure in which a surface in contactwith the substrate and a surface through which light is emitted orreceived are at the top and bottom positions and the light is emitted orreceived in a direction perpendicular to the substrate when it isnormally mounted, the light-emitting or receiving element, the sub-mountsubstrate and the optical waveguide are collectively covered by theresin, the light-emitting or receiving element is mounted on the sidesurface of the sub-mount substrate, and it is mounted on the printedcircuit board. Accordingly, an optical transceiver whose heat generationand power consumption are low can be provided.

In addition, since light can be emitted or received in an arbitrarydirection according to the application, it is possible to provide anoptical transceiver that can be widely applied.

In addition, since the optical transceiver of the present invention hasthe above-described configuration, it can be provided at a low cost.

Moreover, by adopting a configuration where part of the printed circuitboard is covered by the resin, the strength can be increased when it ismounted onto the printed circuit board. As a result, the reliability ofthe apparatus can be improved.

In addition, since bonding wires of the light-emitting and receivingelements are also covered by a resin, the bonding wires can beprotected. As a result, the reliability of the apparatus can beimproved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a light-emitting element (VCSEL).

FIG. 2 is a side view illustrating an example of the structure of aknown optical communication module.

FIG. 3 is a side view illustrating another example of the structure ofthe known optical communication module.

FIG. 4 illustrates a sub-mount substrate in which a light-emitting orreceiving element used in a manufacturing method of an opticalcommunication module of the present invention is mounted on the sidesurface, where (a) is a plan view, (b) is a front view, (c) is a sideview, and (d) is a perspective view.

FIG. 5 is a cross-sectional view illustrating a fiber tape which is anexample of an optical waveguide used in the manufacturing method of theoptical communication module of the present invention.

FIG. 6 is a side view illustrating a final process of the manufacturingmethod of the optical communication module of the present invention.

FIG. 7 is a plan view in which main parts on the side of alight-emitting element (VCSEL) of an optical communication modulemanufactured in a second embodiment are enlarged.

FIG. 8 is a plan view in which main parts on the side of alight-receiving element (PD) of the optical communication modulemanufactured in the second embodiment are enlarged.

FIG. 9 is a perspective view illustrating the optical communicationmodule manufactured in the second embodiment.

FIG. 10 is a view illustrating the eye pattern measured in the secondembodiment.

FIG. 11 illustrates an embodiment of an optical transceiver of thepresent invention, where (a) is a plan view and (b) is a front view.

FIG. 12 is a perspective view illustrating an example of the shape of asub-mount substrate.

FIG. 13 is a front view of main parts illustrating the light-emitting orreceiving direction and the light-emitting or receiving angle θ in amounted state.

FIG. 14 is a plan view illustrating an optical transceiver of areference example.

FIG. 15 is a configuration view illustrating the apparatus outline of ahead mounted display manufactured in a third embodiment related to theoptical transceiver of the present invention.

FIG. 16 is a configuration view illustrating the structure of an opticaltransceiver in the head mounted display of the third embodiment.

FIG. 17 is a configuration view illustrating the apparatus outline of amobile phone manufactured in a fourth embodiment related to the opticaltransceiver of the present invention.

FIG. 18 illustrates the structure of an optical transceiver provided inthe mobile phone manufactured in the fourth embodiment, where (a) is afront view of main parts and (b) is a configuration view illustrating anexample of the relationship between the fiber deviation angle and theamount of increase in height.

FIG. 19 illustrates the angle deviation occurring in the opticaltransceiver, where (a) is a front view of main parts in a state wherethere is no angle deviation, (b) is a front view of main partsillustrating a state of emission angle deviation, and (c) is a frontview of main parts illustrating a state of fiber angle deviation.

FIG. 20 is a cross-sectional view of an optical transceiver manufacturedin a fifth embodiment.

FIG. 21 is a graph illustrating the conditions of a heat cycle testperformed in a fifth embodiment.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

31: SUB-MOUNT SUBSTRATE

32: LIGHT-EMITTING OR RECEIVING ELEMENT (VCSEL OR PD)

33: GOLD WIRE

34: BOTTOM SURFACE ELECTRODE

35: SIDE SURFACE ELECTRODE

41: FIBER TAPE

42: FIBER TYPE OPTICAL WAVEGUIDE

43: TAPING MATERIAL

51: DISPENSER NOZZLE

52: POLYMER CLADDING FIBER

53: SUB-MOUNT SUBSTRATE

54: VCSEL

55: PD

56: PRINTED CIRCUIT BOARD

57: UV-CURABLE RESIN

61: VCSEL

62: SUB-MOUNT SUBSTRATE

63: GOLD WIRE

64: PRINTED CIRCUIT BOARD

65: ELECTRODE

71: PD

72: SUB-MOUNT SUBSTRATE

73: GOLD WIRE

74: PRINTED CIRCUIT BOARD

75: ELECTRODE

76: OPTICAL FIBER

77: IN-CURABLE RESIN

80: OPTICAL COMMUNICATION MODULE

81, 82: PRINTED CIRCUIT BOARD

83: OPTICAL FIBER

100: OPTICAL TRANSCEIVER

101˜103: PRINTED CIRCUIT BOARD

104˜106: SUB-MOUNT SUBSTRATE

107: LIGHT-EMITTING ELEMENT

108: LIGHT-RECEIVING ELEMENT

109: OPTICAL WAVEGUIDE

110: RESIN

111: TAPE SHEET

112A˜112D: SIDE SURFACE

113: BOTTOM SURFACE

114: PRINTED CIRCUIT BOARD

115: SUB-MOUNT SUBSTRATE

116: LIGHT-EMITTING OR RECEIVING ELEMENT

123: HEAD MOUNTED DISPLAY

124: TEST SUBJECT

125: CONTROL DEVICE

126: OPTICAL WAVEGUIDE

127: PRINTED CIRCUIT BOARD

128: SUB-MOUNT SUBSTRATE

129: OPTICAL WAVEGUIDE

130: MOBILE PHONE

131: LIQUID CRYSTAL DISPLAY

132: KEYPAD

133: CAMERA MODULE

134˜135: PRINTED CIRCUIT BOARD

136: OPTICAL WAVEGUIDE

137: SUB-MOUNT SUBSTRATE

138: VCSEL

139: RESIN

140: OPTICAL TRANSCEIVER

141: PRINTED CIRCUIT BOARD

142: SUB-MOUNT SUBSTRATE

143: LIGHT-EMITTING ELEMENT

144: OPTICAL WAVEGUIDE

145: INSIDE RESIN LAYER

146: MIDDLE RESIN LAYER

147: OUTSIDE RESIN LAYER

148: THERMALLY CONDUCTIVE FILLER

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings.

FIGS. 4 to 6 are views illustrating an embodiment of a manufacturingmethod of an optical communication module according to the presentinvention. An item (a) in FIG. 4 is a plan view of a sub-mount substratein which one side of each of a light-emitting element andlight-receiving element (hereinafter, referred to as a light-emitting orreceiving element) is mounted on the side surface, an item (b) in FIG. 4is a front view, an item (c) in FIG. 4 is a side view, and an item (d)in FIG. 4 is a perspective view. FIG. 5 is a cross-sectional viewillustrating the fiber tape as an example of an optical waveguide, andFIG. 6 is a side view illustrating the final process of a manufacturingmethod of an optical communication module.

A manufacturing method of the present invention is characterized in thatthe following processes are sequentially performed; (1) a process ofmounting a light-emitting element and a light-receiving element on aside surface of a sub-mount substrate and mounting the sub-mountsubstrate on a printed circuit board such that the light-emitting andreceiving directions of the light-emitting element and light-receivingelement are parallel to the printed circuit board; (2) a process ofaligning an optical waveguide; and (3) a process of dropping a resinsolution on a sub-mount substrate portion including an optical waveguideend and the light-emitting element or the light-receiving element and ofcuring the resin solution.

First, the process (1) will be described. A state where a light-emittingor receiving element is mounted on a side surface of a sub-mountsubstrate is shown in FIG. 4. In FIG. 4, reference numeral 31 denotes asub-mount substrate, reference numeral 32 denotes a light-emitting orreceiving element (VCSEL or PD), reference numeral 33 denotes gold wire,reference numeral 34 denotes a bottom surface electrode, and referencenumeral 35 denotes a side surface electrode.

In the manufacturing method of the present invention, the sub-mountsubstrate 31 may be formed by using a material, such as aluminum nitrideor aluminum oxide, in order to achieve compatibility between sufficientinsulation and heat dissipation of the heat generated from thelight-emitting or receiving element 32 which is mounted.

In addition, the sub-mount substrate 31 has an electrode pattern on thebottom and side surfaces. The bottom surface electrode 34 is bonded to apredetermined electrode pad on the printed circuit board. An anode and acathode of the light-emitting or receiving element 32 are bonded to theside surface electrode 35.

Usually, the light-emitting or receiving element 32 has a structurewhere at least one of the anode and the cathode is electricallyconnected to an electrode by wire bonding.

Since the gold wire 33 is exposed after bonding, it is typical toprotect the gold wire by quickly applying sealant after wire bonding. Itis desirable that the resin for wire protection not be applied at thispoint of time. In addition, a conductive paste or the like may be usedwhen fixing the light-emitting or receiving element 32 to the sub-mountsubstrate or fixing it to the sub-mount substrate so as to beelectrically conductive. Since the fixing strength of the conductivepaste is low, mold processing using a protective resin is usuallyneeded. However, it is desirable that the protective resin not beapplied at this point of time.

After mounting the light-emitting and receiving elements on the sidesurface of the sub-mount substrate, the sub-mount substrate is mountedon the printed circuit board such that the light-emitting and receivingdirections of the light-emitting and receiving elements are parallel tothe printed circuit board. A state where the light-emitting or receivingelement is mounted onto the printed circuit board is shown in FIG. 6. Asshown in FIG. 6, a sub-mount substrate 53, in which a VCSEL 54 that is alight-emitting element is mounted on the side surface, is mounted on aprinted circuit board 56 such that the light-emitting direction of theVCSEL 54 is parallel to a printed circuit board 56, and the sub-mountsubstrate 53, in which a PD 55 that is a light-receiving element ismounted on the side surface, is mounted on the printed circuit board 56such that the light-emitting direction of the PD 55 is parallel to theprinted circuit board 56.

As a means for transporting a sub-mount substrate onto a printed circuitboard, it is industrially desirable to use suction type tweezers for themounting of electronic components. Therefore, with regard to the shapeof the sub-mount substrate, a top surface thereof is smooth ispreferable. When mounting the sub-mount substrate on the printed circuitboard, powder or conductive paste may be used. Particularly whenconductive paste is used, mold processing using a protective resin isusually needed because the fixing strength of sub-mount substrate is notsufficient. However, it is desirable that the protective resin not beapplied at this point of time.

Next, (2) will be described. In the manufacturing method of the presentinvention, a sheet type optical waveguide, a fiber type opticalwaveguide, or the like may be used as an optical waveguide. Particularlyin the case of the fiber type optical waveguide, a long waveguide can bemanufactured. Accordingly, it is advantageous in that an opticalwaveguide can be obtained cheaply. A silica glass fiber, a plasticfiber, and the like may be used as the fiber type optical waveguide. Inaddition, it may also be possible to use a polymer cladding fiber whichis a kind of silica glass fiber and in which the core, through whichlight is guided, is formed of silica glass and a cladding portion aroundthe core is formed of polymer. A plural number of such fiber typewaveguides may be collectively mounted by taping and cabling.

FIG. 5 is a view illustrating a fiber tape as an example of the fibertype optical waveguide. This fiber tape 41 has a configuration in whichfour fiber type optical waveguides 42 are aligned and are collectivelycoated in the tape form by a taping material 43 formed of a syntheticresin. For example, two-way communication lines may be mounted and fixedat once by mounting a light-emitting element and a light-receivingelement on a sub-mount substrate and by taping the silica glass fiberaccording to the distance between the light-emitting portion and thelight-receiving portion. In addition, handling efficiency, heatresistance, strength, and the like of the optical waveguide may beimproved by taping and cabling.

As an alignment method of the optical waveguide, either active alignmentor passive alignment is possible. A method of setting alignment marks ona sub-mount substrate and an optical waveguide and performing alignmentwhile performing image recognition with a mounting machine isindustrially preferable. In case of using the fiber type opticalwaveguide, the handling performance of suction tweezers of the mountingmachine can be improved by taping the fibers.

Next, (3) will be described. In the process (3), a resin solution isdropped onto the sub-mount substrate portion having the opticalwaveguide end and the light-emitting or receiving element and is cured.

This makes it possible to simultaneously a) protect the bonding wireprotruding from the light-emitting or receiving element, b) ensure thestrength of the mounting of the light-emitting or receiving element ontothe sub-mount substrate, c) fix the optical waveguide, and d) ensure thestrength of the mounting of the sub-mount substrate onto the printedcircuit board.

As resins used herein, an epoxy-based resin, an acrylic-based resin, asilicone-based resin, a polyimide-based resin, a polysilane-based resin,and the like may be used. Examples of the curing method include UVcuring, heat curing, two solution mixing (chemical reaction) curing, andmoisture reaction curing. In particular, the UV-curable resin ispreferable since the curing time is short and positional deviationbetween the optical waveguide and the light-emitting or receivingelement does not occur easily during the curing.

In the present invention, coupling loss between the light-emitting orreceiving element and the optical waveguide can be reduced by preventingFresnel reflection using a resin whose refractive index after curing isthe same as that of the core of the optical waveguide. For example, aresin whose refractive index after curing is 1.40 to 1.60 is preferablyused when the silica glass optical fiber is used as the opticalwaveguide. In addition, a stabilized optical transmission characteristiccan be achieved by using a resin whose thermal expansion coefficientafter curing is close to those of the sub-mount substrate, opticalwaveguide, and printed circuit board. Particularly by using a resinwhose thermal expansion coefficient is close to that of the printedcircuit board, the stabilized optical transmission characteristic can beachieved. Moreover, there is also the effect that the light-emitting orreceiving element is sealed from the air, in addition to a) to d). As aresult, the stabilization of the optical transmission characteristic ispossible.

FIG. 6 is a view illustrating a state of execution of the process (3).In this drawing, reference numeral 51 denotes a dispenser nozzle fordropping a resin solution, reference numeral 52 denotes a polymercladding fiber (fiber type optical waveguide), reference numeral 53denotes a sub-mount substrate, reference numeral 54 denotes a VCSELwhich is a light-emitting element, reference numeral 55 denotes a PDwhich is a light-receiving element, reference numeral 56 denotes aprinted circuit board, and reference numeral 57 denotes a UV-curableresin. In this illustration, the first sub-mount substrate 53 in whichthe VCSEL 54 is mounted on the side surface and the second sub-mountsubstrate 53 in which the PD 55 is mounted on the side surface aremounted on the printed circuit board 56 such that the light-emittingdirection or light-receiving direction of each of them is parallel tothe printed circuit board 56, the polymer cladding fiber 52 is disposedin a state where the ends thereof are adjacent to a light-emittingportion of the VCSEL 54 and a light-receiving portion of the PD 55, andthe UV-curable resin 57 is dropped from the tip of the dispenser nozzle51 and is cured such that both ends of the polymer cladding fiber 52,and the VCSEL 54 and the PD 55 are sealed. Then, after the curing of theresin, the VCSEL 54 or the PD 55 is mounted on the printed circuit board56 such that the light-emitting direction or light-receiving directionof each of them is parallel to the printed circuit board 56 and they areoptically coupled by the polymer cladding fiber 52, therebymanufacturing the optical communication module.

As shown in FIG. 6, the optical communication module manufactured asdescribed above has the printed circuit board 56, the sub-mountsubstrate 53 in which one or both the VCSEL 53 that is a light-emittingelement and the PD 55 that is a light-receiving element are mounted onthe side surfaces, and an optical waveguide (polymer cladding fiber 52)provided between the VCSEL 53 and the PD 55 so as to be able to beoptically coupled with these elements, and is characterized in that theVCSEL 53 and the PD 55 are mounted on the printed circuit board 56through the sub-mount substrate 53 such that the light-emitting andreceiving directions of them are parallel to the printed circuit board56 and the VCSEL 53 and the PD 55 of the sub-mount substrate 53 and theends of the optical waveguide adjacent to them are covered by theUV-curable resin 57.

This optical communication module can emit and receive light in thedirection parallel to the printed circuit board 56. Accordingly,reduction in height (thickness) and miniaturization of the opticalcommunication module can be realized.

Next, an embodiment of the optical transceiver of the present inventionwill be described.

FIG. 11 illustrates an embodiment of the optical transceiver of thepresent invention. An item (a) in FIG. 11 is a plan view of an opticaltransceiver 100, and an item (b) in FIG. 11 is a front view. In thisdrawing, reference numeral 100 denotes an optical transceiver, referencenumerals 101 to 103 denote printed circuit boards, reference numerals104 to 106 denote sub-mount substrates, reference numeral 107 denotes alight-emitting element, reference numeral 108 denotes a light-receivingelement, reference numeral 109 denotes an optical waveguide, referencenumeral 110 denotes a resin, and reference numeral 111 denotes a tapesheet.

The optical transceiver 100 of the present embodiment has the printedcircuit boards 101 to 103, the sub-mount substrate 104 in which both thelight-emitting element 107 and the light-receiving element 108 aremounted, the sub-mount substrate 105 in which the light-emitting element107 is mounted on the side surface, the sub-mount substrate 106 in whichthe light-receiving element 108 is mounted on the side surface, and theoptical waveguide 109 provided between the light-emitting element 107and the light-receiving element 108 so as to be able to be opticallycoupled with these elements, and is characterized in that thelight-emitting element 107 and the light-receiving element 108 each havestructures in which a surface in contact with the substrate and asurface, through which light is emitted or received, are at the top andbottom positions and the light is emitted or received in a directionperpendicular to the mounted substrate, the light-emitting element 107and the light-receiving element 108 are mounted on the printed circuitboards 101 to 103 through the sub-mount substrates 104 to 106 such thatthe light-emitting and receiving directions of them are notperpendicular to the printed circuit boards 101 to 103, and all of thesub-mount substrates 104 to 106, the entire light-emitting element 107,the entire light-receiving element 108, and the ends of the opticalwaveguide 109 adjacent to them are collectively covered by the resin110.

The optical transceiver 100 of the present embodiment has a structure inwhich the light-emitting elements and the light-receiving elementsmounted on the three printed circuit boards 101 to 103 are connected toeach other by the two fiber type optical waveguides 109 as shown inFIGS. 11A and 11B. This is different from an optical transceiver with astructure in which a sub-mount substrate 118, in which both alight-emitting element 119 and a light-receiving element 120 are mountedon one side surface, is mounted on a printed circuit board 117, theselight-emitting and receiving elements are joined to an optical waveguide121 which is bent in a U shape, and the entire sub-mount substrate 118,all of the light-emitting element and the light-receiving element, andboth ends of the optical waveguide 121 are collectively covered by aresin 122 like a reference example of FIG. 14.

As shown in FIG. 1, the light-emitting element 107 and thelight-receiving element 108 each have structures in which a surface incontact with a support substrate (sub-mount substrate) and a surface,through which light is emitted or received, are at the top and bottompositions and light is emitted or received in a direction perpendicularto the substrate when they are normally mounted. Among light sourceswith such a structure, as a light source which allows optical wiring tobe applied to high-speed communication apparatuses such as servers,optical wiring in automobiles, and small electronic apparatuses such asmobile phones, there is, for example, a vertical cavity surface emittinglaser (VCSEL). A laser having the above structure is low in height inthe light-emitting and receiving directions and has a feature in thatits price is cheap compared with a known LD. In addition, because of thestructure of the device, a threshold current for emission is low. As aresult, it has a feature in that its power consumption is low. For theabove application, a light source which is cheap and has low powerconsumption is a great advantage.

The shape of each of the sub-mount substrates 104 to 106 has at least asurface, which is mounted on each of the printed circuit boards 101 to103, and a surface which is not parallel to the surface and on which thelight-emitting or receiving element is mounted. Side surfaces 112 a to112 d of the sub-mount substrates 104 to 106 indicate all surfaces,which are not parallel to a surface 113 mounted on the printed circuitboard, among the surfaces which form the shapes of the sub-mountsubstrates 104 to 106, as shown in FIG. 12. By mounting theabove-described light-emitting or receiving elements on the sidesurfaces 112 a of the sub-mount substrates 104 to 106, it has a functionof setting the light-emitting or receiving direction of thelight-emitting or receiving element in an arbitrary direction other thanthe direction perpendicular to the printed circuit boards 101 to 103.

In the known optical transceiver, in order to emit and receive light inan arbitrary direction with respect to the printed circuit board, theoptical path had to be changed using an optical component, such as amirror. The optical path changing component, such as a mirror, is notdesirable because it is expensive. Moreover, in an optical pathconverter, the coupling efficiency of light is lowered due to scatteringand the like, which is disadvantageous. An optical transceiver, in whicha light-emitting surface and a light-receiving surface are at the topand bottom positions and which can emit and receive light in anarbitrary direction other than a direction perpendicular to the printedcircuit board using a light-emitting or receiving element having astructure in which light is emitted or received in a directionperpendicular to the substrate when it is normally mounted, isgroundbreaking since it is possible to reduce the setting space of theoptical transceiver and optical waveguide. In addition, when it isplaced near a movable portion, bending of the optical waveguide can bereduced. Accordingly, it is also advantageous from the point of view ofreliability and the bending loss of the optical waveguide.

Materials with sufficient electrical insulation properties, for example,an aluminum nitride and an aluminum oxide may be used as materials ofthe sub-mount substrates 104 to 106. Since these materials are excellentin thermal conductivity, the heat generated from the light-emittingelement can be efficiently dissipated.

In addition, the sub-mount substrates 104 to 106 have electrode patternson the bottom and side surfaces, as shown in FIGS. 4A to 4D. The bottomsurface electrode 34 is bonded to a predetermined electrode pad on eachof the printed circuit boards 101 to 103. An anode and a cathode of alight-emitting or receiving element are bonded to the side surfaceelectrode 35 (refer to FIGS. 4A to 4D). Usually, the light-emitting orreceiving element has a structure where at least one of the anode andthe cathode is electrically connected to an electrode by wire bonding.

One or both the light-emitting element and the light-receiving elementare mounted on the side surfaces of the sub-mount substrates 104 to 106,and the sub-mount substrates 104 to 106 are mounted on the printedcircuit boards 101 to 103. As a result, the light-emitting or receivingdirection of the light-emitting or receiving element is a directionother than the direction perpendicular to the top surfaces of theprinted circuit boards 101 to 103.

A sheet type optical waveguide, a fiber type optical waveguide, or thelike may be used as the optical waveguide 109. Particularly in the caseof the fiber type optical waveguide, a long waveguide can bemanufactured. Accordingly, it is advantageous in that an opticalwaveguide can be obtained cheaply. A silica glass fiber, a plasticfiber, and the like may be used as the fiber type optical waveguide. Inaddition, it may also be possible to use a polymer cladding fiber whichis a kind of silica glass fiber and in which the core, through whichlight is guided, is formed of silica glass and a cladding portion aroundthe core is formed of polymer. A plural number of such fiber typeoptical waveguides may be collectively mounted by taping and cabling.

Also in the illustration shown in FIGS. 11A and 11B, part of a pluralnumber of optical waveguides 109 on the printed circuit board is tapedby collectively covering it with the tape sheet 111.

As an alignment method of the optical waveguide 109, either activealignment or passive alignment is possible. A method of settingalignment marks on the sub-mount substrates 104 to 106 and the opticalwaveguide 109 and performing alignment while performing imagerecognition with a mounting machine is industrially preferable. In caseof using the fiber type optical waveguide, the handling performance ofsuction tweezers of the mounting machine can be improved by taping aplural number of fibers.

An epoxy-based resin, an acrylic-based resin, a silicone-based resin, apolyimide-based resin, a polysilane-based resin, and the like may beused as the resin 110 which covers collectively all of the sub-mountsubstrates 104 to 106, the entire light-emitting element 107, the entirelight-receiving element 108, and the ends of the optical waveguide 109adjacent to them. Examples of the curing method include UV curing, heatcuring, two solution mixing (chemical reaction) curing, and moisturereaction curing. In particular, the UV-curable resin is preferable sincethe curing time is short and positional deviation between the opticalwaveguide 109 and the light-emitting or receiving element does noteasily occur during the curing. Covering the entire parts with the resin110 indicates a state where the resin is also applied to the printedcircuit boards 101 to 103 as shown in FIG. 11. As described above, byadopting the structure in which the entire main parts are collectivelycovered with the resin 110, the following can be performedsimultaneously; a) protection of the bonding wire protruding from thelight-emitting or receiving element, b) ensuring the strength of themounting of the light-emitting or receiving element onto the sub-mountsubstrate, c) fixing of the optical waveguide, and d) ensuring thestrength of the mounting of the sub-mount substrate onto the printedcircuit board. As a result, it is possible to ensure low cost, lowheight, and high reliability.

Coupling loss between the light-emitting or receiving element and theoptical waveguide 109 can be reduced by preventing Fresnel reflectionusing the resin 110 whose refractive index after curing is the same asthat of the core of the optical waveguide 109. For example, the resin110 whose refractive index after curing is 1.40 to 1.60 is preferablyused when the silica glass optical fiber is used as the opticalwaveguide 109. In addition, a stabilized optical transmissioncharacteristic can be achieved by using the resin 110 whose thermalexpansion coefficient after curing is close to those of the sub-mountsubstrates 104 to 106, the optical waveguide 109, and the printedcircuit boards 101 to 103. Particularly by using a resin whose thermalexpansion coefficient is close to that of the printed circuit board, thestabilized optical transmission characteristic can be achieved.Moreover, there is also an effect that the light-emitting or receivingelement is sealed from the air, in addition to a) to d). As a result,the stabilized optical transmission characteristic is possible.

The resin 110 is dropped onto a predetermined place and is cured. Adispenser and the like may be used for the dropping.

Although this optical transceiver 100 is configured as a device thatemits and receives light in an arbitrary direction which is notperpendicular to the printed circuit boards 101 to 103, this angle isdefined with reference to FIGS. 12 and 13. In FIGS. 12 and 13, assumingthat a direction parallel to a printed circuit board 114, that is, thebottom surface 113 of a sub-mount substrate 115 mounted on the printedcircuit board 114 is 0° and the side surfaces 112 a to 112 d on which alight-emitting or receiving element 116 is mounted is a plus side, thelight-emitting or receiving angle θ formed by the bottom surface 114 ofthe printed circuit board 114 and the light-emitting or receivingdirection can be expressed as −90° to 90°. Here, θ=−90° and 90°indicates a direction perpendicular to the printed circuit board 114.

When the light-emitting or receiving angle θ is parallel to the printedcircuit board 114 (θ=0°), the total height of the optical transceiver isits lowest. It is suitable for optical wiring inside thin mobileapparatuses, such as mobile phones and notebook PCs. FIG. 11 images thecase where the light-emitting or receiving angle θ is 0°.

The polymer cladding fiber mentioned as an example of the opticalwaveguide 109 is a fiber type optical waveguide with a core-claddingstructure in which the core portion is formed of silica glass and thecladding portion is formed of a polymeric material. Since the coreportion is silica glass, the polymer cladding fiber shows a hightransmission characteristic. Since the cladding portion is formed of apolymeric material, that is, since the diameter of the glass portionwhich forms the fiber is small, the fiber can be bent with smallercurvature.

In addition, a polymer waveguide may also be used as the opticalwaveguide 109. This polymer waveguide is a waveguide with acore-cladding structure in which both the core and the cladding areformed of a polymeric material. From the process of manufacture, thecross-sectional shape of the waveguide is a rectangle and in the shapeof tape form. Since it is flexible, routing and fixing are easy.

In the optical transceiver 100, the resin 110 is not limited to thesingle-layer structure and may have a structure in which resin layers oftwo or three or more layers are laminated.

In addition, when the resin layer 110 is configured to include aplurality of resin layers, a thermally conductive filler may also bemixed in the outermost resin layer. Thus, by mixing the thermallyconductive filler in the outside resin layer, an effect such that theheat generated from the light-receiving element or the light-emittingelement is dissipated to the outside is improved. As a result, since atemperature change in the inside resin layer caused by generation ofheat of the light-emitting or receiving element is reduced, it ispossible to solve the problems of deviation of the optical axis ordamage of the light-receiving element or light-emitting element.Material and shape of the thermally conductive filler are notparticularly limited. For example, a carbon filler and the like may beused. In this case, the inside resin layer is formed of a resin which istransparent to the communication light. Although the material of thetransparent resin is not particularly limited, an epoxy resin, anacrylic resin, and the like may be used. Since the inside resin layerserves to perform alignment of the light-receiving element or thelight-emitting element and the optical waveguide and to fix them, theshort curing time is better. When the curing time is long, there is apossibility that optical axis deviation will occur during the curing.

In addition, a configuration may be adopted where the resin 110 isformed as a three-layer resin layer and the refractive index of theinside resin layer is higher than that of the middle resin layer. Byadopting such a structure, the inside resin layer and the middle resinlayer form the core-cladding structure. As a result, the couplingefficiency of the light-receiving element or the light-emitting elementand the optical waveguide is improved. In addition, by mixing theabove-described thermally conductive filler in the outside resin layer,an effect that the heat generated from the light-receiving element orthe light-emitting element is dissipated to the outside is improved. Asa result, temperature changes in the inside resin layer and middle resinlayer caused by generation of heat of the light-emitting or receivingelement is reduced.

In this case, the middle resin layer is formed of a resin which istransparent to the communication light, similar to the inside resinlayer. Although a material of the transparent resin is not particularlylimited, an epoxy resin, an acrylic resin, and the like may be used.

In addition, a configuration may be adopted where the resin 110 isformed as a three-layer resin layer and a transparent filler is mixed inthe inside resin layer (and the middle resin layer). Due to thetransparent filler of the inside resin layer (and the middle resinlayer), the coefficient of linear expansion of a bonding portion betweenthe light-receiving element or the light-emitting element and theoptical waveguide end is low. Accordingly, the problems of deviation ofthe optical axis or damage of the light-receiving element orlight-emitting element can be effectively solved.

In this case, although it is needless to say, it is preferable that therefractive index of the transparent filler used for the inside resinlayer be the same or almost the same as the refractive index of theresin used for the inside resin layer. If a difference between both therefractive indices increases, scattering becomes noticeable. This is notdesirable because the loss of communication light is increased. Amaterial of the transparent filler is not particularly limited. When thewavelength used for communication is that of visible light tonear-infrared light, a silica glass filler may be used. The shape of thetransparent filler may be a needle shape, a grain shape, and the likeand is not particularly limited. However, as disclosed inJP-A-2006-257353, it is preferable that the shape be spherical andcapable of suppressing the scattering of communication light by avoidinga region where Mie scattering, in which the particle diameter is oneseveral of the wavelength to several times of the wavelength, easilyoccurs.

Also when using a transparent filler in the middle resin layer, it ispreferable to use a transparent filler with a refractive index close tothat of the resin used for the middle resin layer, similar to the caseof the inside resin layer.

When the resin 110 having a plurality of layers is provided, it ispreferable that the inside resin layer be provided to completely coverat least the entire light-emitting or receiving element, the entiresub-mount substrate, and the optical waveguide end. This makes itpossible to improve the bonding strength between the light-receivingelement or the light-emitting element and the optical waveguide and toimprove the strength when the sub-mount substrate is mounted onto theprinted circuit board. Accordingly, the reliability can be improved. Inaddition, when the transparent filler is mixed in the inside resinlayer, the coefficient of linear expansion of the inside resin layer islow. Accordingly, since it becomes more resistant against temperaturechange, the reliability can be further improved.

First Example

The sub-mount substrate shown in FIG. 4 was manufactured. A material ofthe sub-mount substrate was an aluminum nitride. An electrode materialon the sub-mount substrate was a gold tin alloy in consideration of thebonding strength between the electrode material and gold wire whenmounting a light-emitting or receiving element.

As shown in FIG. 4, the light-emitting or receiving element was mountedon the sub-mount substrate. This mounting was performed with conductivesilver paste and gold wire. A VCSEL with an emission center wavelengthof 850 nm was used as the light-emitting element, and a PD was used asthe light-receiving element.

Then, the sub-mount substrate in which the light-emitting or receivingelement was mounted on the side surface was mounted on the printedcircuit board. Transport of the sub-mount substrate was performed byvacuum tweezers, and it was bonded to an electrode pad of the printedcircuit board using conductive silver paste.

Then, alignment and fixing of the optical waveguide was performed. Apolymer cladding fiber in which the diameter of the core formed ofsilica glass was 50 μm was used for the optical waveguide. Afluorine-containing polymer was used for the cladding of the polymercladding fiber. The alignment was performed in the active alignmentmethod by actually operating the VCSEL and the PD.

Then, the resin was dropped onto the optical waveguide end and thesub-mount substrate portion and was cured. As the resin, a UV-curableresin was used whose refractive index after curing was 1.45. As shown inFIG. 6, an appropriate amount of resin was dropped using an airdispenser so that an optical waveguide end, the VCSEL, the PD, and thesub-mount substrate are fixed. After the dropping of the resin, UV lightwas irradiated for curing to thereby manufacture the opticalcommunication module.

Using the manufactured optical communication module, the transmissiontest was performed. At a VCSEL driving speed of 1 GHz, it was driven for4 hours and there was no error.

Second Example

A video transmission test was performed using the optical communicationmodule which was actually manufactured according to the manufacturingmethod of the present invention.

As a light-emitting element, a vertical cavity surface emitting laser(VCSEL) with a luminous wavelength of 850 nm and a cutoff frequency of2.5 GHz was used. As shown in FIG. 1, a commercially available VCSEL wasselected which was of a type where the cathode is connected to anelectrode by wire bonding and the anode is connected to an electrodeusing conductive paste.

As a light-receiving element, a GaAs photodiode (PD) with a cutofffrequency of 2.5 GHz was used. Similar to the VCSEL, a commerciallyavailable PD with a shape where the cathode is made to be electricallyconductive by wire bonding and the anode is made to be electricallyconductive by conductive paste was selected.

The same sub-mount substrate as the one described in the first examplewas used as the sub-mount substrate. The VCSEL and the PD were mountedon the sub-mount substrate using the conductive silver paste and thegold wire.

Then, the sub-mount substrate in which the VCSEL and the PD were mountedon the side surface was mounted. Transport of the sub-mount substratewas performed by vacuum tweezers, and it was bonded to an electrode padof the printed circuit board using conductive silver paste.

FIG. 7 is an enlarged view of a bonding portion when the sub-mountsubstrate, in which the VCSEL is mounted on the side surface, is mountedon the printed circuit board. In FIG. 7, reference numeral 61 denotes aVCSEL, reference numeral 62 denotes a sub-mount substrate, referencenumeral 63 denotes gold wire, reference numeral 64 denotes a printedcircuit board, and reference numeral 65 denotes an electrode. Asdescribed in the explanation of the above embodiment, neither a moldresin for protecting the gold wire connected to the VCSEL nor a moldresin for improving the bonding strength between the VCSEL and thesub-mount substrate nor a mold resin for improving the bonding strengthbetween the sub-mount substrate and the printed circuit board wasapplied at this point of time.

Then, the optical waveguide, the VCSEL, and the PD were aligned andfixed.

A commercially available multi-mode silica glass fiber was used as theoptical waveguide. The light propagating core diameter of the glassfiber was 50 μm.

The alignment was performed in the active alignment method by actuallyoperating the VCSEL and the PD. After performing the alignment, anappropriate amount of UV-curable resin whose refractive index aftercuring was 1.45 was dropped onto the bonding portion of the opticalfiber and the VCSEL and the PD and ultraviolet light with a wavelengthof 365 nm was irradiated to cure the resin. A commercially availableresin was used as the UV-curable resin. Dropping of the resin wasperformed using the air dispenser similar to the first example.

FIG. 9 is an enlarged view of a bonding portion of a PD and an opticalfiber after curing of the UV resin. In FIG. 9, reference numeral 71denotes a PD, reference numeral 72 denotes a sub-mount substrate,reference numeral 73 denotes gold wire, reference numeral 74 denotes aprinted circuit board, reference numeral 75 denotes an electrode(printed circuit board), reference numeral 76 denotes an optical fiber,and reference numeral 77 denotes a UV-curable resin.

As described in the above explanation of the embodiment, protection ofthe gold wire connected to the PD, improvement in the bonding strengthbetween the PD and the sub-mount substrate, and improvement in thebonding strength between the sub-mount substrate and the printed circuitboard can be realized by the UV-curable resin which fixes the opticalfiber and the PD.

The entire configuration of the optical communication modulemanufactured as described above is shown in FIG. 10. In FIG. 10,reference numeral 80 denotes the optical communication modulemanufactured in this example, reference numeral 81 denotes a printedcircuit board on which either a VCSEL or a PD is mounted through asub-mount substrate, reference numeral 82 denotes a printed circuitboard on which either a VCSEL or a PD is mounted through a sub-mountsubstrate, and reference numeral 83 denotes an optical fiber connectedto both the printed circuit boards such that the VCSEL and the PDthereof can be optically coupled.

A transmission test was performed using the optical communicationmodule. The bit error rate in light signal transmission betweenVCSEL—optical fiber—PD was measured using a commercially availabledigital data analyzer. At a driving speed of 2.5 GHz, it was driven for4 hours and there was no error.

In addition, the eye pattern was measured using a commercially availablesampling oscilloscope. FIG. 10 shows the measured eye pattern. From theeye pattern shown in FIG. 10, it was confirmed that sufficient openingwas obtained in this optical communication module.

In addition, a transmission test of an image signal was performed usingthe optical communication module. The transmission was performed in theLVDS method after converting an analog signal output from a CCD camerainto a digital signal and then serializing it. Analog conversion,serializing, and LVDS-corresponding signal conversion were performedusing a commercially available board for communication. As a result ofthe test, an image of the CCD camera could be transmitted in real timeand be displayed on the display.

Third Example

An optical transceiver was applied between a head mounted display 123and its control device 125. The schematic configuration is shown in FIG.15. This apparatus is the goggle type head mounted display 123 that atest subject 124 wears on the head and is fitted and fixed to the outerperiphery of one ear. An optical waveguide 126 is taken out from therear of the portion fixed to the ear. In order to improve a feeling offitting to the eye and due to the restrictions in design, as shown inFIG. 16, an extracted portion of the optical waveguide 126 has astructure including a printed circuit board 127 provided at the rear endof the head mounted display 123, a sub-mount substrate 128 mounted onthe printed circuit board 127, a light-emitting or -receiving elementmounted on the side surface of the sub-mount substrate 128, and anoptical waveguide 129 which is connected to the element so as to be ableto be optically coupled. Since the head mounted display 123 is small,the printed circuit board 127 of the optical transmitting set is housedat the position shown in FIG. 16. Accordingly, the optical waveguide 129and the optical transmitting set substrate are not level to each other,and a predetermined angle is formed therebetween. In the test apparatusof this example, an angle of about 50° is formed. As an opticaltransmitting set applied herein, an optical transmitting set wasprepared whose emission angle with respect to the printed circuit board127 was 50°. This was mounted in the head mounted display test apparatusand the transmission test was performed. For comparison, an opticaltransmitting set whose emission angle was 0° was prepared and evaluated.

First, the transmission test was performed in a state where the opticaltransmitting set is mounted in the head mounted display 123. The biterror rate in light signal transmission between VCSEL—optical fiber—PDwas measured using a commercially available digital data analyzer. At adriving speed of 1.5 GHz, it was driven for 4 hours and there was noerror. In addition, the eye pattern was measured using a commerciallyavailable sampling oscilloscope, and it was confirmed that sufficientopening was obtained.

For comparison, the same test was also performed in the opticaltransmitting set whose emission angle was 0°. As a result, there was noerror in a state where the head mounted display 123 was held still.However, when the test subject 124 walked in a state where it wasactually mounted on the ear of the test subject 124, turbulence in theeye pattern was large and stable transmission was not possible. When theoptical transmitting set was mounted whose emission angle(light-emitting or receiving angle θ) was 0°, it could be seen that theexcessive force was applied to the optical fiber base in the opticalwaveguide 129 extracted portion of the head mounted display 123 and thereliability was reduced.

Fourth Example

The optical transceiver was applied for the wiring lines in a mobilephone 130. The schematic configuration is shown in FIG. 17. In thedrawing, reference numeral 130 denotes the mobile phone, referencenumeral 131 denotes a liquid crystal display, reference numeral 132denotes a key pad, reference numeral 133 denotes a camera module,reference numerals 134 and 135 denote printed circuit boards, andreference numeral 136 denotes an optical waveguide.

In thin electronic apparatuses including mobile phones, it is necessarythat the height of a component mounted on the printed circuit board be 1mm or less, and there is a demand for further reduction in height. Byapplying an optical transmitting set and an optical receiving set withlight-emitting and -receiving angles of 0° in order to meet such ademand, an optical transceiver with a height of 0.7 mm from the printedcircuit board which includes a light-emitting or -receiving element, anoptical waveguide, and a fixing resin can be realized. The configurationof the apparatus is shown in an item (a) in FIG. 18. In the item (a) inFIG. 18, reference numeral 135 (134) denotes a printed circuit board,reference numeral 136 denotes an optical waveguide, reference numeral137 denotes a sub-mount substrate, reference numeral 138 denotes a VCSELwhich is a light-emitting element, and reference numeral 139 denotes aresin which collectively covers them.

In addition, the sizes a to f of the respective portions in the item (a)in FIG. 18 were as follows. a=0.70 mm, b=0.50 mm, c=0.30 mm, d=0.25 mm,e=0.10 mm, f=0.25 mm. A silica glass fiber with an external diameter of80 μm was used as the optical waveguide 136. This silica glass fiber hasan external diameter of 125 μm by coating the outer side with aUV-curable urethane resin. In addition, a UV-curable epoxy resin wasused as the resin 139.

The sub-mount substrate 137 was manufactured by an injection moldingmethod using the liquid crystal polymer. Mounting of the light-emittingor receiving element onto the sub-mount substrate 137, mounting of thesub-mount substrate 137 onto the printed circuit boards 134 and 135, andmounting of the optical waveguide 136 onto the printed circuit boards134 and 135 were performed using an automatic machine (mounter) formounting electronic components. Since there is a size error in aninjection-molded product and a mounting position accuracy error in anautomatic machine, an error occurs according to the capability of themounting machine even if an optical transceiver with a light-emitting or-receiving angle of θ=0° is manufactured. In this test, in order toinvestigate the tolerance to the manufacture error, a sampleintentionally inclined in the range of −3° to 3° was also manufactured.

In addition, since fiber angle deviation may also occur as shown in anitem (b) in FIG. 18 in addition to emission angle deviation andreceiving angle deviation, a sample with fiber angle deviation in therange of −3° to 3° was also manufactured. In addition, the fiberdeviation angle is defined as an angle formed by the centerline of thefiber and a top surface of the printed circuit board.

When the sizes a to f of the respective portions in the item (a) in FIG.18 are taken into consideration, it can be seen that a sufficientreduction in height can be realized even if the emission angle deviatesby several degrees. In addition, a transmission test was performed usingthe optical transceivers with the deviations. As a result, atransmission characteristic which was not inferior and which wassufficiently stabilized compared with the optical transceiver with nodeviation could be realized. For example, when the fiber deviation angleis 5° in the fiber deviation shown in the item (b) in FIG. 18, a heightincrement g is 0.03 mm or less which results in only a slight increase.

FIG. 19 illustrates the patterns of angle deviation thought to occur inthe optical transceiver shown in the item (a) in FIG. 18. An item (a) inFIG. 19 is a front view of main parts of an optical transceiver with noangle deviation, an item (b) in FIG. 19 is a front view of main partsillustrating a state of emission angle deviation, and an item (c) inFIG. 19 is a front view of main parts illustrating a state of fiberangle deviation. In addition, although the emission angle deviation whenthe VCSEL 138 is mounted is illustrated in the item (b) in FIG. 19, thesame is true for the receiving angle deviation when a light-receivingelement, such as a PD, is mounted.

Causes of the occurrence of the emission/receiving angle deviationinclude deviation when the sub-mount substrate 137 is mounted on theprinted circuit board 135 (134) and deviation when the light-emitting or-receiving element is mounted on the sub-mount substrate 137. The item(b) in FIG. 19 corresponds to the former deviation.

In the optical transceiver of the present invention, it could be seenthat practically sufficient light transmission and reception functionscould be realized if it is an angle deviation of several degreesincluding the angle deviation shown in FIGS. 19( b) and 19(c).Presumably, the reason is that the coupling efficiency between thelight-emitting or -receiving element and the optical waveguide can beimproved by comparatively rough optical axis alignment and a change inthe coupling efficiency caused by the physical stress from the outsideis small since the light-emitting or -receiving element and the opticalwaveguide end are collectively fixed by the resin whose refractive indexwas controlled. Accordingly, in manufacturing the optical transceiver ofthe present invention, it is thought that they are substantially thesame modules even if there is a deviation of several degrees.

Fifth Example

As shown in FIG. 20, an optical transceiver 140 was manufactured whichhad a structure where a sub-mount substrate 142, in which alight-emitting element 143 or a light-receiving element was mounted onthe side surface, was mounted on a printed circuit board 141, one end ofan optical fiber type optical waveguide 144 was joined to thelight-emitting element 143, and the entire light-emitting element 143,the entire sub-mount substrate 142, and the end of the optical waveguide144 were covered with three resin layers of an inside resin layer 145, amiddle resin layer 146, and an outside resin layer 147 in which athermally conductive filler 148 was mixed.

As the light-emitting element 143, a VCSEL with an emission centerwavelength of 850 nm was used. As the inside resin layer 145, anultraviolet curable epoxy resin was used whose refractive index aftercuring was 1.457 and in which 10 mass % of silica glass filler, whoserefractive index was adjusted, was mixed. As the middle resin layer 164,an ultraviolet curable epoxy resin was used whose refractive index aftercuring was 1.452 and in which 10 mass % of silica glass filler, whoserefractive index was adjusted, was mixed. As the outside resin layer147, an ultraviolet curable epoxy resin was used in which 10 mass % ofcarbon filler as the thermally conductive filler 148 was mixed. As theoptical waveguide 144, an optical fiber formed of silica glass was used.

A sample using an epoxy resin, which did not contain a filler in each ofthe inside, middle, outside resin layers, was also manufactured forcomparison.

A heat cycle test was performed for the manufactured sample. The testwas performed by making the VCSEL emit light with emission output of 0.3mW. 500 cycle processing was performed, with the diagram shown in FIG.21 as 1 cycle, and bonding portions between the VCSEL of the sampleafter the processing, the resin layer, and the optical fiber wereobserved with an optical microscope.

In samples (with no filler) manufactured for comparison, a small numberof samples were found in which a bonding portion between the VCSEL andthe resin and a bonding portion between the optical fiber and the resinpeeled off. In samples in which the filler was added to the resin layer,there was hardly any bonding peeling found. As a result, it was seenthat the sample, in which the filler was added to the resin layer, wasresistant against the heat cycle.

Moreover, in the fifth embodiment, a commercially available filler wasused as the silica glass filler. When it is difficult to adjust therefractive index with a commercially available silica glass filler, itis possible to use it after synthesizing the silica glass filler using agas phase synthesis method. As a raw material, a silicon tetrachloride,for example, may be used. A spherical silica glass filler can beobtained by mixing the vapor of the silicon tetrachloride with a carriergas, such as argon and nitrogen, and oxygen, transporting it to asynthesis chamber, and heating it up to 800° to 1500°. In order toadjust the refractive index of the silica glass filler, for example, itis preferable to mix the vapor of germanium tetrachloride, aluminumtrichloride, and the like with the vapor of the silicon tetrachlorideand to synthesize it. Elements, such as germanium and aluminum, canincrease the refractive index of silica glass when added to the silicaglass. The amount of increase in the refractive index may be adjustedaccording to the amount added.

INDUSTRIAL APPLICABILITY

According to the manufacturing method of the optical communicationmodule of the present invention, a thin and small optical communicationmodule can be produced efficiently and cheaply.

1. An optical communication module comprising: a printed circuit board;a sub-mount substrate in which one or both a light-emitting element anda light-receiving element are mounted on a side surface thereof; and anoptical waveguide provided between the light-emitting element and thelight-receiving element so as to be able to be optically coupled withthe light-emitting element and the light-receiving element, wherein thelight-emitting element and the light-receiving element are mounted onthe printed circuit board with the sub-mount substrate there betweensuch that the light-emitting and -receiving directions of the elementsare parallel to the printed circuit board, and the light-emittingelement and the light-receiving element of the sub-mount substrate andends of the optical waveguide adjacent to the elements are covered by aresin.
 2. The optical communication module according to claim 1, whereinthe resin is a UV-curable resin.
 3. The optical communication moduleaccording to claim 1, wherein the optical waveguide is one or two ormore selected from a silica glass fiber, a polymer cladding fiber, and aplastic fiber.
 4. The optical communication module according to claim 1,wherein the optical waveguide is a silica glass fiber or a polymercladding fiber, and the refractive index of the resin after curing iswithin a range of 1.40 to 1.60.
 5. The optical communication moduleaccording to claim 1, wherein the optical waveguide is a polymercladding fiber in which the diameter of the core formed of silica glassis 100 μm or less.
 6. The optical communication module according toclaim 1, wherein the optical waveguide is a fiber tape with a tapeshape, and an alignment mark for alignment is provided on the fibertape.
 7. A manufacturing method of an optical communication module formanufacturing the optical communication module, comprising thesequentially performed steps of: (1) mounting a light-emitting elementand a light-receiving element on a side surface of a sub-mount substrateand mounting the sub-mount substrate on a printed circuit board suchthat the light-emitting and -receiving directions of the light-emittingelement and light-receiving element are parallel to the printed circuitboard; (2) aligning an optical waveguide; and (3) dropping a resinsolution on an area of the sub-mount substrate including an opticalwaveguide end and the light-emitting element or the light-receivingelement, and curing the resin solution.
 8. The manufacturing method ofan optical communication module according to claim 7, wherein the resinis a UV curable resin.
 9. The manufacturing method of an opticalcommunication module according to claim 7, wherein the optical waveguideis one or two or more selected from a silica glass fiber, a polymercladding fiber, and a plastic fiber.
 10. The manufacturing method of anoptical communication module according to claim 7, wherein the opticalwaveguide is a silica glass fiber or a polymer cladding fiber, and therefractive index of the resin after curing is within a range of 1.40 to1.60.
 11. The manufacturing method of an optical communication moduleaccording to claim 7, wherein the optical waveguide is a polymercladding fiber in which the diameter of the core formed of silica glassis 100 μm or less.
 12. The manufacturing method of an opticalcommunication module according to claim 7, wherein the optical waveguideis a fiber tape with a tape shape, and an alignment mark for alignmentis provided on the fiber tape.
 13. An optical transceiver comprising: aprinted circuit board; a sub-mount substrate in which one or both alight-emitting element and a light-receiving element are mounted on aside surface thereof; and an optical waveguide provided between thelight-emitting element and the light-receiving element so as to be ableto be optically coupled with the light-emitting 5 element and thelight-receiving element, wherein the light-emitting element and thelight-receiving element each have structures in which a surface incontact with the substrate and a surface, through which light is emittedor received, are at the top and bottom positions and the light isemitted or received in a direction perpendicular to the mountedsubstrate, the light-emitting element and the light-receiving elementare mounted on the printed circuit board with the sub-mount substratetherebetween such that the light-emitting and receiving directions ofthe elements are not perpendicular to the printed circuit board, and theentire sub-mount substrate, the entire light-emitting element, theentire light-receiving element, and ends of the optical waveguideadjacent to the elements are collectively covered by a resin.
 14. Theoptical transceiver according to claim 13, wherein the resin also coversa part of the printed circuit board.
 15. The optical transceiveraccording to claim 13, wherein bonding wire for conducting an electriccurrent to the light-emitting element and the light-receiving element iscollectively covered by the resin.
 16. The optical transceiver accordingto claim 13, wherein the optical waveguide is one or two or moreselected from a group including a silica glass fiber, a polymer claddingfiber, a plastic fiber, and a polymer waveguide.
 17. The opticaltransceiver according to claim 13, wherein the optical waveguide is asilica glass fiber, and the refractive index of the collectivelycovering resin after curing is within a range of 1.40 to 1.60.
 18. Theoptical transceiver according to claim 13, wherein the light-emittingand receiving directions of the light-emitting element andlight-receiving element are parallel to the printed circuit board. 19.The optical transceiver according to claim 13, wherein the resinconsists of two layers or three or more layers.
 20. The opticaltransceiver according to claim 19, wherein a thermally conductive filleris mixed in the outermost layer of said resin having two layers or threeor more layers.